Installation programs allow an end user to customize the installation of an application software program so that it is optimized for his particular computer system and so that it best meets his perceived needs within the constraints imposed by his computer system. The process typically proceeds in the following manner: the installation program engages in a dialog with the user by presenting him with a series of screen displays, each of which requests that he select one of several available installation options. As a consequence of such dialog, the installation program defines a unique set of installation steps which are followed in setting up the application program on the user's computer system. The steps generally specify the mass storage device to which application files will be copied, and are also likely to define a subset of available application modules which will be copied. The installation steps may also set operating system configuration parameters. Typically, such an installation process is encapsulated in what is known in the software industry as a script file. The installation program's installer-processing engine reads the script file, displays the dialog screens to the user in the order listed in the script file, and proceeds with the installation, a step at a time, as mandated by the user's response to each of the dialog screens.
There are several drawbacks to the installation process heretofore described. One drawback is that script files are generally hand written, which makes the process prone to error. A further drawback is difficulty posed by the need to test and debug code external to the script during the install/uninstall process. Developers often have a need to write such code, which when executed, performs tasks useful during the development process.
An even more serious drawback related to script-based installation programs is that the installation of a multiple-component application program is tied to a single script file. Thus, the system configuration steps, the component selection steps, the screen dialogs presented to the user, and the installation process flow are all interrelated. Modification of any aspect of the installation process would almost certainly require a rewriting of the script file. Because of the interrelated nature of the script-based installation process, changes to one part of the script file may have a ripple effect on the entire installation process, making rewriting the script file a complicated and tedious task.
Another serious drawback is that the installer-processing engine has access to only the features or functionality provided in the script file. Thus, modifications to the installation process which are not defined in the script file, such as modifying existing components in an undefined manner, replacing an already installed component with an updated component, or adding one or more new components would, most likely, be impossible without a complete rewriting of the script file.
Another drawback of script-based installation technology is the need to include, within the script file, logic that is used to determine whether or not a particular component is installed, as well as logic that will determine which configuration settings should be made. Installation criteria logic may also be employed to determine whether or not a particular software component can be installed on a particular operating system, or whether or not a specific configuration setting already exists.
A final limitation of the current script-based installation programs is their inability to download updated components from the Internet. Current installer technology does not support integrated installation over the Internet, nor does it support the addition of new software at run time.
Uninstallation of the application software is beset by many of the same limitations which affect installation. Uninstallation programs also employ a script file, which is read by an uninstaller-processing engine. Generally speaking, uninstallation of a complex, multi-component software package is limited to uninstalling all of the installed components. Though there are situations that require the removal of only a portion of installed components, the current script-based technology does not support partial uninstallations.